For three decades, biosensors have been the subject of increasing research efforts and constitute now a major component of mainstream analytical chemistry (see e.g. Turner et al. (Eds.), Biosensors: Fundamentals and Applications, Oxford University Press, New York, 1987; Guilbault et al. (Eds.), Uses of Immobilized Biological Compounds, vol. 252, NATO ASI, Kluver Academic Publishers, 1993; Wang, Anal. Chem. 67 (1995) 487 R.) Considerable effort has been devoted in particular to develop optimized techniques for immobilizing biomolecules on suitable supports. Since miniaturized transducers are gaining importance, much attention is focused on the development of procedures allowing the spatially controlled deposition of biomolecules (see e.g. Heiduschka et al., Chem. Eur. J. 2 (1996) 667; Jobst et al., Anal. Chem. 68 (1996) 3173.)
Among conventional immobilization procedures, only the entrapment of biomolecules in electrogenerated conducting polymer films offers a good spatial resolution (see e.g. Bartlett et al., J. Electroanal. Chem. 363 (1993) 1; Schuhmann, Mikrochim. Acta, 121 (1995) 1; Trojanowicz et al., Mikrochim. Acta, 121 (1995) 167; Cosnier, Electroanalysis, 9 (1997) 894). However, the biomolecule entrapment within electropolymerized films suffers from severe drawbacks. This method requires high concentrations of biomolecules in the aqueous electrolyte during the electropolymerization process. This is because biomolecule incorporation in the growing polymer is only due to the presence of enzyme in the immediate vicinity of the electrode surface. In addition, the physical entrapment in polymer films such as polypyrrole, polythiophene, polyacetylene or polyaniline, drastically reduces the accessibility to the immobilized biomolecule. The steric constraints generated by the surrounding polymer in particular may hinder the formation of specific antigen-antibody binding. Consequently, the electrochemical entrapment of biomolecules is not an ideal method for the fabrication of immunosensors.
Other relevant prior art is U.S. Pat. No. 5,837,859 to Teoule et al., incorporated herein by reference, and the corresponding WO 94/22889.